If you are living on the edge and are already done testing the RC1 5600 build, head on over to http://download.windowsvista.com/preview/rc1/en/download-5728.htm and see about the latest published 5728 build.
Please heed the following advice from the site:
"This build (5728) has a number of improvements and updates from RC1, but has not been put through the same internal testing process as RC1 and therefore may be unstable in certain installations. We are making this release available for a limited time only (and only by download) in order to get broad distribution and testing in a variety of PC configurations. Please note: This build may not have the same level of support or servicing via Windows Update, and you may not be able to upgrade to the final version of Windows Vista."